TeamCity 10.0.2 –
Something that isn’t mentioned in this article or the most up to date article for installing addition plugins here: https://confluence.jetbrains.com/display/TCD10/Installing+Additional+Plugins
I used the upload plugin zip feature within the web application. I chose the zip file and named it “NET Core” and it refused to get picked up from TeamCity after restarting. Nothing was in the TeamCity logs. Before I contacted support and after ripping out some hair, I browsed to the plugins folder and renamed the file from “NET Core” to “NETCore.zip” and TeamCity finally picked it up! Either it was having a problem with the space in the file name or missing the zip extension, either way, this has to be a bug.